The U.S. Department of Agriculture Wednesday released a new plant hardiness zone map.

Cacti won't be growing in Central New York gardens anytime soon.

But some areas may be able to grow peaches, different varieties of grapes or a Southern magnolia tree.

The U.S. Department of Agriculture Wednesday issued its new Plant Hardiness Zone Map, last updated in 1990. Syracuse and most of Central New York moved from zone 5a to zone 5b, which means winter is warmer than it used to be. Parts of Oswego and Auburn moved from zone 5b to the warmer 6a zone. The lower the number, the colder it is.

The multi-colored map in gardening catalogs and on seed packets helps the country's estimated 80 million gardeners, as well as farmers and horticulture businesses, identify where and when plants grow best.

Hardiness zones represent the average annual extreme minimum temperature during a 30-year period. In zone 5a, the lowest temperature on average was between minus 15 and minus 20 degrees Fahrenheit. In zone 5b, the coldest temperature is 10 to 15 degrees below zero. In 6a, the lowest temperature is minus 5 to minus 10.

In some cases -- Ohio, Nebraska and Texas -- nearly the entire states have been updated to warmer zones. The map also creates two new zones: 12, for climates with average lows of 50 to 60 degrees and 13, for lows of 60 to 70 degrees.

The map is also designed to be "Internet-friendly," according to the USDA. Type in your zip code on the interactive map on the USDA website, planthardiness.ars.usda.gov, and you can find out what zone you're in, down to half-mile segments. Static copies of the map may be downloaded to personal computers.

The new map is much more sophisticated than the old one because of advances in technology and can't be exactly compared to the old map, Kim Kaplan of the Agriculture Research Service in Washington said during a online seminar announcing the new map.

The new map uses 30 years of temperature data, from 1976 to 2005. The 1990 map was based on temperature data from 1974 to 1986.

The new map also takes into account topography -- slope, elevation, prevailing winds and proximity to water -- for the first time.

But if your hardiness zone has changed in the new map, don't start pulling plants out of your garden or change what you are growing, the USDA said.

Zone maps "are a bunch of hooey," said Terry Ettinger, greenhouse manager at State University of New York College of Environmental Science and Forestry. Hardiness maps are only one of a myriad of things people should take into consideration when deciding what to plant, he said.

Microclimates may be too small to show up on the map, he said. And each yard and garden has its own microclimates. One side of your house may be colder than the other. The wind may clear snow from one part of your yard but pile it up in another. One part of your yard may be lower and wetter than another. All of those factors can influence what plants will thrive and which will not, he said.

Wind, soil type, soil moisture, humidity, pollution, snow and winter sunshine can affect the survival of plants. The way plants are placed in the landscape, how they are planted and their size and health might also influence their survival.

Nina Bassuk, professor of horticulture and program leader of Cornell's Urban Horticulture Institute, said the hardiness map is a good place to start when deciding what to plant, but then you have to look at other differences, such as the north or south side of your house.

In Ithaca, for example, trees that thrive downtown may not survive at the top of the hill where Cornell is located, she said.

The new USDA plant hardiness map updates this one, made in 1990.

Her area of study is urban landscapes, particularly trees. She uses Ithaca as "my downtown lab."

The new zone map shows that urban areas tend to be "heat islands," where concrete, asphalt and other factors keep temperatures warmer than surrounding rural and suburban areas.

As Ithaca has gotten warmer, trees such as willow oaks and cold-hardy varieties of Southern magnolia have survived,, she said.

"We're always looking for more types of trees that could do well in urban areas," she said. "With a slightly warmer climate, you can have a much more diverse planting palette."

Perhaps the biggest change for Upstate New York is that zone 6 is creeping farther south from the shores of Lake Ontario, she said.

"The warmer area near Lake Ontario has bled south, following the Finger Lakes," she said. "Warmer winters are extending as far down as Ithaca and Watkins Glen."

While Bassuk said the new map will not have a "huge impact" for gardeners, it may encourage them to try to grow plants they might not have tried before.

"People may look a little bit further afield," she said. "In some areas, peaches will do better now than they would have."

Parts of Upstate are "right on the fringe of the difference between growing apples versus peaches,'" said David Wolfe, professor of plant and soil ecology at Cornell University.

The temperature change may create opportunities for other crops. Finger Lakes wineries may be able to diversify the grapes they grow, he said.

Wolfe also sees the warmer temperatures in the new zone map as another piece of evidence to prove that the earth's climate is changing, a stance the USDA is downplaying.

"The map is not a good instrument for determining climate change," Kaplan said. "In some cases where areas changed zones there was less than a one-degree change in temperature."

"I would not be so cautious as the USDA was," Wolfe said. "Taken with prior maps and other evidence, it corroborates that there is climate change."

The trend toward warmer temperatures is "part and parcel of climate change," he said. Winter lows that creep upward mean more pests will survive to destroy grains, oilseeds and other crops during growing seasons, he said.

Bassuk said she's been having fun playing with the new interactive map.

"What I like about new map is that it gives you much more resolution. On the interactive map you can zoom in and zoom out. ... You can move around the whole country that way. The interactive is the most fun," she said.

"Sometimes you'll see things that were not possible to see when we only had the big map. People may have the confidence to try some plants they might not have tried before."